In electrical insulating materials for motors, it has recently demanded to have heat resistance at high temperature and hydrolysis resistance. For example, new alternatives for cooling medium have been proposed as electrical insulating materials for motors used in refrigerators and air conditioners, in connection with abolition of specific chlorofluorocarbons from an environmental problem. Such cooling medium and its compatible lubricant easily absorb water, so in the above-mentioned insulating materials, there is a demand for hydrolysis resistance in addition to heat resistance. In electrical insulating materials for motors used in hybrid cars, water is infiltrated into the materials under usage environment, so there is a demand for hydrolysis resistance in addition to heat resistance.
A polyarylene sulfide film has excellent features such as heat resistance, flame retardancy, rigidity, chemical resistance, electrical insulating properties and low hygroscopicity and is used particularly preferably in electrical instruments, electronics, machine parts and automobile parts.
In recent years, application of a polyphenylene sulfide (hereinafter abbreviated sometimes as PPS) film to electrical insulating materials proceeds to make use of its electrical insulating properties and excellent low hygroscopicity. For example, (1) use of a biaxially oriented film as an electrical insulating material is known (see Patent Document 1). Further, (2) a non-oriented PPS sheet is also known (see Patent Documents 2 and 3). In addition, (3) a laminate comprising a biaxially oriented PPS layer laminated on a non-oriented PPS layer without an adhesive is known (see Patent Documents 4 and 5).
However, the conventional film, sheet, laminated film and laminate described above have the following problems. That is, the film in the item (1) above may be unsatisfactory in tensile elongation at break, impact resistance and tear propagation strength, and when used for example as a motor slot liner or as a wedge, causes film breakage or delamination in some cases. The non-oriented PPS sheet in the item (2) above is excellent in tear propagation strength, but is extremely poor in tensile elongation at break and lowers its strength rapidly at a temperature near to the melting point, thus significantly deteriorating shape retention in some cases. The laminate in the item (3) above is laminated without an adhesive to increase the film thickness thereby increasing the stiffness of the film, but the adhesive strength of laminate interface is insufficient so the tensile elongation at break is low thus causing a problem in processability in some cases.
As described above, the polyphenylene sulfide film is poor in ductility and tensile elongation at break, thus making its applications limited at present, and its improvement is strongly desired. For a method of improving its ductility, a resin composition or a film having other thermoplastic resin mixed in polyphenylene sulfide is proposed. For example, a composition comprising nylon 11 and nylon 12 dispersed as particles having an average diameter of 1 μm or less (see Patent Document 6), a composition comprising PPS, polyamide and epoxy resin (see Patent Document 7), a composition comprising PPS and polyamide (see Patent Documents 8 and 9), a film comprising PPS and polyether imide (see Patent Document 10), a film comprising PPS and polysulfone (see Patent Document 11) etc. are disclosed, but a resin composition or a film having thermoplastic resin such as polyamide or polysulfone dispersed ultra-finely in the range of 10 to 500 nm in PPS is not described. On the other hand, a resin composition having thermoplastic resin such as polyamide dispersed ultra-finely in a characteristically dispersed state is proposed (see Patent Document 12). However, this resin composition has formed a structure by shear field-dependent phase solubilization/phase separation wherein the resin is destabilized again in a non-shear state to cause phase separation after it is once compatibilized in a shear field at the time of melt-kneading, and when a sheet or film is formed, its structural stability is not sufficient in some cases, and the appropriate method for forming a biaxially oriented film is not described.    Patent Document 1: Japanese Unexamined Patent Publication No. 1980-35456    Patent Document 2: Japanese Unexamined Patent Publication No. 1981-34426    Patent Document 3: Japanese Unexamined Patent Publication No. 1982-121052    Patent Document 4: Japanese Unexamined Patent Publication No. 1990-45144    Patent Document 5: Japanese Unexamined Patent Publication No. 1992-319436    Patent Document 6: Japanese Unexamined Patent Publication No. 1991-81367    Patent Document 7: Japanese Unexamined Patent Publication No. 1984-155462    Patent Document 8: Japanese Unexamined Patent Publication No. 1988-189458    Patent Document 9: Japanese Unexamined Patent Publication No. 2001-302918    Patent Document 10: Japanese Unexamined Patent Publication No. 1992-146935    Patent Document 11: Japanese Unexamined Patent Publication No. 1987-121761    Patent Document 12: Japanese Unexamined Patent Publication No. 2003-113307